Different types of Dilavar studs?
 

I'm taking apart my 89 3.2 for a top end and reseal job. During disassembly I discovered that all 12 bottom cyl head studs are painted black. Great!, I thought, someone was here before and replaced the studs with original porsche steel studs. But...I also discovered that these bottom studs are non-magnetic which means Dilavar correct?

I have replaced Dilavar on my previous 78SC 3.0 and they were bare metal and not painted or coated (they were also broken). So the question is: are there different types of Dilavar studs? Did porsche improve them by painting or coating them to prevent the corrosion that leads to breakage of these studs?

And finally, this motor is very clean with no corrosion on any of the fastners or cyl head studs. I had no breakage issues while taking the heads off. My understanding is that the factory used Dilavar for its ideal heat expansion rate. If the Dilavars are a newer version and they are coated and not showing any signs of corrosion, should you still replace them just as a precaution?

Dilivar studs in the 3.2 are prone to breakage. If yours were not broken, you were lucky. Replace your lower studs with OEM steel studs.

Yes, later Dilavar studs were coated. The current best Dilavar studs (993) are coated too.

I rebuilt my 86 Carrera engine and left the Dilivar studs (black like yours) in place. I worried about it for awhile but didn't have any issues. They are expensive to replace with 993 dilivars, but if I were doing it again I'd replace the bottom row. I use stock steel studs on my racing engine and they work ok but I've had to retorque them after a few races.

-Andy

I find it interesting that the 993 studs are a recommended replacement and that they, too are Dilivar. Apparently Porsche felt that the thermal expansion properties of Dilivar were important enough to continue to use this material even after many engines suffered failures. I don't hear anyone complaining of 993 stud failures. Is this because of the different design of the 993 studs or is it the coating that prevents corrosion which caused the failures in the Dilivar studs? Does anyone know the reason for threading the entire stud on the 993 version? I would think that would cause more stress risers but I'm not an engineer. It would be interesting to find out if the Dilivar stud failures are mostly the early studs and if the coated studs have a lower failure rate. So far, in my experience with dilivar, my 3.0 (non-coated dilivars) broke and my 3.2 (coated dilivar) is intact.

The coating is the main improvement. The thermal expansion thing is important but the drawback to Dilavar is it is very susceptable to corrosion so that coating needs to be kept intact. The all-thread means the expansion and strain is more evenly distributed along the length of the stud, so it actually has less of a stress riser in a way.

My -84 3.2 snapped a stud last year. I repaced all with supertec studs.

I recently had a late 3.2 in my shop with (8) broken, coated, Dilivar studs. I just tore down a 3.6 with (1) broken, coated Dilivar stud. The remaining Dilivar studs on that motor all have coating chips on them.

The 993 Dilivar studs are a completely different design than the early ones.

Replace all your studs with Supertec head studs.
I have then in all 4 of my engines.
They are designed with modern engineering principles, are cost effective and have a life time guarantee.
The best part is that they are sold by our host.

Did my engine rebuild at 88,000 miles due to 2 broken Dilivar studs that were coated with black. I believe that Dilivar studs will eventually break. Not all of them but if it is 25% your odds of it happening are pretty good. i used steel for the bottom row. Of course that is my humble opinion :D

If the budget had allowed I would have done the Supertec studs.

For a stock rebuild, the OEM steel studs are an acceptable replacement for the lower Dilivar studs.

Supertec Head Studs here on my SC engine, highly recommended and reasonably priced for the lifetime guarantee.

I pulled all 12 Dilivars today. Not a single one broke during removal. The Supertec kit is tempting but not sure I can justify the cost for a stock motor. I wonder if it would be possible to use 1/2 the Supertec set just for the Dilivar exhaust replacements? Apparently Porsche thought only the hotter exhaust side needed the Dilivar expansion properties...

Has anyone besides Eagledriver had any head torque issues with steel studs?

Steel studs will be fine in a stock motor.

Steel studs are quite adequate on an unmodified motor. Of course that said Raceware studs are superior to them and help if you are the kind to worry.

When you say "fine" is that like it's "fine" to marry an ugly woman if you don't have any other choice? :confused:

Fine = maintaining the cylinder head seal while not pulling out of the case (or deforming the case) and not breaking for the desired lifespan.

Whether the stock ones are "fine" I cannot say, but as an engineer you have to know what "good enough is".

You act like the Supertech head studs at 20 hp. :)

I am neither an engineer or an engine builder but I am a long time Porsche owner with plenty of experience with failed engine rebuilds.
When I pay my hard earned money on a rebuilt engine, I look for the best solution possible under each situation.
There is more to performance than hp (IE: longevity to me is paramount) and the best solution that I've seen for cylinder to head stability is the Supertec head stud.
Before Supertec studs we saw most engines, driven with any spirit, leak (sweat) from the head to cylinder seal. With Supertec studs (my last 4 engine including a 3.5 400+ hp turbo) we don't see this phenomenon. Could it be that Supertec builds a superior engine? perhaps but for my money I choose to take as few risks as possible.

I already married the pretty woman and now she has my credit card and she's headed for the mall... :eek:

Well then if the stud had not pulled or broken the preload was not great enough.